I'd better remind you: I just crossdress, and I don't really
understand the
need that drives transsexuals. This is definitely an outsider's
point of view, but hopefully a helpful point of view nonetheless.

Aside from the arguments against CDing, I only know of one (quasi-)Christian
argument against transsexualism:

"If God had meant you to be a woman (or man), He would have made you that
way."

Also known as...

"If man had been meant to fly, he would have been born
with wings."

It's an old idea: that God is a champion of the status quo,
that He despises change.

I could see this idea becoming popular in any other faith... but I cannot
imagine how it became common among Christians.

"Abram, if God wanted you to live in Canaan, you would have been born
there. Jacob, if God wanted you to lead your family, you would have been
the firstborn. Ruth, if God wanted you to be a Jew, you wouldn't
have been born a Moabite. Saul, if God wanted you to be king, you
wouldn't have been born into the least clan of the smallest tribe.
Peter, if God wanted
you to spend your life preaching, you would have been born a priest."

"Human, if God wanted you
to share in eternity, you wouldn't have been
born into a fallen world."

If God has decided He doesn't like transformations anymore - if He
thinks everyone should remain as they were born - He must be awfully
embarrassed about some of the things He did in the Bible.

John 9:1-7

Now as Jesus passed by, He saw a man who was blind from birth.

And His disciples asked Him, saying, "Rabbi, who sinned, this man or his
parents, that he was born blind?"

Jesus answered, "Neither this man nor his parents sinned, but that the works
of God should be revealed in him.

"I must work the works of Him who sent Me while it is day; the night is
coming when no one can work."

"As long as I am in the world, I am the light of the world."

When He had said these things, He spat on the ground and made clay with the
saliva; and He anointed the eyes of the blind man with the
clay.

And He said to him, "Go, wash in the pool of Siloam (which is translated,
Sent). So he went and washed, and came back seeing.

"Jesus, justify this man's status for us. Explain that it is God's will that
he be this way." Wrong, says Jesus. God's will is that every infirmity be
healed, every wrong be set right.

Ponder this: not a single person who went to Jesus for healing was sent away
without it. Not one was left as they were. Never once did Jesus say, "It
is God's will that you be thus."

God is NOT the champion of the world-that-is. God is He who brings about
the world as it should be. As Christians, change is our very life. We were
dead; we are transformed
into life. We must be transformed into the image of Christ; we must be
rebuilt in the likeness of God. God shall not leave us as we found us; where
would we be if He did? Never imagine that the living, transforming Lord God
clings to the way things have been.

On a less spiritual level...

People born weak excercise to become strong. People born ill or crippled
go to doctors to become well. People born ugly go to plastic surgeons to
become beautiful (in theory) (and perhaps surrendering to vanity in the
process, but that's another discussion). Hair is dyed, birthmarks are
removed, and nobody complains that God's will is being violated. Someone
who actually believed that God opposed the modification of the body would
really have their work cut out for them.

Or perhaps something about the sex organs makes them particularly off-limits;
perhaps this is the one body part that may not be changed? Unlikely. He
commanded the Israelite men to be circumcised, purely for the purpose of
signalling their identity as His people.